To answer this question, we need to understand the concept of HTML tags.

Option A) DT - This option is incorrect because the <dt> tag is used to define a term in a description list, but it is not a two-sided tag.

Option B) LI - This option is incorrect because the <li> tag is used to define a list item in an ordered or unordered list, but it is not a two-sided tag.

Option C) DD - This option is incorrect because the <dd> tag is used to define a description in a description list, but it is not a two-sided tag.

Option D) DL - This option is correct because the <dl> tag is used to define a description list in HTML. It is a two-sided tag because it has an opening <dl> tag and a closing </dl> tag.

Therefore, the correct answer is option D) DL. This option is correct because the <dl> tag is a two-sided tag.